Effects of the physicochemical properties of biochar and soil on moisture sorption

Abstract

To investigate the correlation between the physicochemical and hygroscopic properties of biochar and soil, the moisture sorption properties of typical biochars and soils were observed inside a thermostatically controlled incubator at a temperature of 30 °C and humidity of 70%. Results showed that the equilibrium moisture content (EMC) of tobacco stem biochar, rice husk biochar, Hubei paddy soil, and Jiangxi red soil were 7.66%, 6.40%, 3.34%, and 2.92%, respectively. There was a synergistic interaction between biochar and soil, resulting in a higher EMC of biochar-soil mixtures with increases ranging from 0.16% to 2.52%. The porosity of tobacco stem biochar, rice husk biochar, Hubei paddy soil, and Jiangxi red soil were 82.58%, 65.05%, 59.02%, and 56.71%, respectively. Additionally, according to our findings, the biochar had higher carbon content, C/N ratio, and carbonyl groups, and lower bulk density, oxygen content, O/C ratio, and carboxyl groups than the soil. The linear correlation analysis indicated that there was a positive correlation between EMC and the physicochemical properties of biochar and soil, including porosity, carbon content, nitrogen content, and carboxyl groups. Consideration of the physicochemical properties of biochar and soil will significantly improve the overall properties of biochar used for soil amendment.